Meperidine as a discriminative stimuli in rats and pigeons will be analyzed to determine which meperidine analogues will be generated to the meperidine cue, which drugs can block the discriminative effects of meperidine, and how these results compare with the relatively potent and pure narcotic, fentanyl. We will be comparing these results to behavioral effects obtained with the convulsant agents, normeperidine (a metabolite of meperidine), naloxone (a narcotic antagonist which is a GABA antagonist at high doses), and picrotoxin (a GABA antagonist). We will be evaluating a series of central depressants for their ability to block the non-narcotic effects of meperidine and related analogues. Pentobarbital has proven to be effective, and diazepam and clonazepam, upon acute and chronic administration, are currently being evaluated. Further studies will evaluate the effectiveness of representative anticonvulsants, phenytoin, baclofen, sodium valproate, aminooxyacetic acid (AOAA), ethosuximide, and trimethadione. These studies will help in finding drugs which will be clinically effective in reversing non-narcotic effects of meperidine-related agents. We want to determine if the non-narcotic effects of the phenylpiperidine analgesics are related to an antagonist effect of GABA. Thus we will also be studying the interaction of these agents with muscimol, the GABA agonist.